The present invention is directed to methods of benzylation and benzylated compositions from polyamines for curing epoxy resin.
Various methods have been used to reduce the carbamation in epoxy processing by reducing the amount of primary amines. One method includes adducting amines with mono glycidyl ethers. However, this method has the disadvantage of increasing the viscosity of the product. An additional method includes making a Michael addition of acrylonitrile on the primary amine. In that case the viscosity remains low but a retro reaction occurring, in time, releases free acrylonitrile, which makes the product highly toxic and difficult to handle.
Other methods have been tested with limited success, such as making a Mannich base by reaction of the polyamine with formaldehyde and phenol. In such cases a substantial amount of phenol is left that makes the product toxic. This toxicity can be reduced by reacting tris-dimethylaminomethylphenol (K-54) with an amine in a transaminification reaction where by the amine displaces the dimethyl amine (DMA) which is distilled and collected for recycling. This reaction suffers from the drawback of undesirably high viscosity.
U.S. Pat. No. 7,396,902 B2, which is hereby incorporated by reference in its entirety, discloses a curing agent for epoxy resin that is produced from styrenation of meta xylylene diamine or 1,3-BAC (1,3-bis(aminomethyl)cyclohexane. The U.S. Pat. No. 7,396,902 Patent suffers from the drawback that the styrenation process is complicated and arduous.
Benzylated aminopropylated ethylenediamines and benzylated polyalkylene polyamines, as well as the uses thereof are generally disclosed in U.S. Patent Application Publications 2009/0030125 and 2009/0029175, which are hereby incorporated by reference in their entirety. The reactions and products formed in the 2009/0030125 and 2009/0029175 result in a wide range of products and properties, where it is desirable in the art to have greater tailorability and specific product specifications in the resultant benzylated products.
U.S. Pat. No. 3,634,316, which is hereby incorporated by reference in its entirety, discloses a method for forming antiozonant xylylenediamine derivative. The method includes dehydrohalogenation of halogenated alkyls with xylylenediamine. An exemplary relevant claim, is claim 2, where an antiozonant is claimed that is N,N′-dibenzyl-m, and p-xylylenediamine. The product from the U.S. Pat. No. 3,634,316 Patent, for example, in claim 2, is a dibenzylated product, the manufacture of which is not specified. The U.S. Pat. No. 3,634,316 Patent does not disclose the formed compounds use in crosslinking agents to crosslink and harden epoxy resins. In addition, the U.S. Pat. No. 3,634,316 Patent does not disclose or provide a method in which the properties are adjustable or tailorable.
When epoxy resins are cured with most non-aromatic amines, the miscibility of these amines with the epoxy resins is not always good and some incomplete cure can take place. To improve the cure, some diluents such as benzyl alcohol can be used. This introduces a solvent in the system and the resulting system is considered as emissive, meaning that once it will be cured raw materials will be emitted from the coating over time. Due to the introduction of more stringent laws, non-emissive coatings have become more valued.
It is also known that the presence of plentiful primary amines will increase the amount of carbamation experienced by the coating at lower temperatures and higher relative humidity. In order to overcome these problems, the amines have been adducted with monoglycidyl ethers particularly the phenyl glycidyl ether or the o-cresyl glycidyl ether. These reactions are very advantageous to lower the vapor pressure and improve the miscibility of the amine to the resin; unfortunately this adduction tends to increase the viscosity to a very high level which can hinder the application of the product. This type of adduction might also require the removal of the free amine. Should the adduction be carried out far enough to remove all free amine, the viscosity would become much too high and in some cases the product would even be solid. This type of adduction is also limited as each molecule used per molecule amine will remove a reactive site, which can diminish the cross-linking density of the systems particularly with amines having only four or less reactive sites.
There are numerous amine-based curing agents and amine-epoxy compositions that are employed in the amine-epoxy coating industry; however, known products fail to completely address the needs or solve the problems noted above. Accordingly, it is to this end that the present invention is directed. Specifically, methods for making epoxy curing agents and cured epoxy products having reduced carbamation, reduced toxicity and not suffering from the above drawbacks would be desirable in the art.